Copper and Calcium Uptake in Colored Hair

During hair coloring, disulfide bonds in cystine were oxidized to create cysteic acid, forming binding sites for metal ions such as Ca2+ and Cu2+ from tap water. This increased metal uptake negatively impacted fiber properties, reducing shine and causing poor wet and dry feel. Additionally, copper uptake contributed to further fiber damage during subsequent coloring due to metal-induced radical chemistry. Using nanoscale secondary ion mass spectrometry (NanoSIMS), researchers located calcium and copper within colored hair, finding high concentrations of calcium in the cuticle region, particularly in sulfur-rich areas. Untreated hair served as a baseline for comparison.